1. Field of the Invention
The present invention concerns a joining structure for frames, and more specifically a highly stable and secure joining structure for couplings and pipes in frames used in bicycles and similar vehicles.
2. Prior Art
Conventionally, frames used in bicycles and similar vehicles have been constructed by joining couplings and pipes, and then securely bonding the couplings and pipes together by welding or brazing.
With the spread of sport bicycles in recent years, however, efforts have been made to lighten the weight of bicycle bodies. As a result, frames have been constructed from aluminum alloys and various frames using new materials such as carbon fibers, etc., have been developed. In the case of such new materials, the melting point may be low (as in aluminum alloys), or heating may cause embrittlement or a change in color or shape so that the external appearance of the material deteriorates. In some cases, therefore, joining by welding or brazing is impossible. Accordingly, the couplings and pipes in such frames are joined together by means of a bonding agent. As a result, there has also been active research and development concerning bonding agents with high bonding strength.
In the case of a mere chemical adhesive force which depends on a bonding agent, there are problems in durability when the bicycle is loaded. As a consequence, the frame may break while the bicycle is being ridden, resulting in personal injury. Accordingly,the combined use of some other locking means in addition to the aforementioned bonding agent is desirable. Furthermore, in cases where only a bonding agent is used, the axial length of the connecting extenions of the couplings is short, so that the area coated with the aforementioned bonding agent is small. Accordingly, even if a strong bonding agent is used, some uncertainty remains regarding the bonding strength.